Z Bed operation. Or, My Z Motion Control Fantasy

Machine: K40 with Lightobject Z-Bed

Board: Cohesion3D Laserboard

Firmware: Cohesion3D Board Smoothie, as delivered

Problem/ Question - How X and Y work out of the box: When I open LightBurn and power on my K40, the X and Y home-to-switches sequence begins, moving the laser output head from wherever to the rear and left positions of X and Y. When it’s done, we know the 2 physical dimensional positions of X and Y. That’s X=0 and Y=210 in my case. From this we can derive our physical origin, X=0 and Y=0. These positions are used to reference laser travel anywhere within our cut/burn space in 2 dimensions of workspace. Yay!

How Z works out of the box: Z, on the other hand, doesn’t move. It just resets its position to 0, regardless of where it was when last powered down. It doesn’t matter where the Z device, the Z-bed, is. Z always resets to start at 0 when the K40 turns on and LightBurn is opened. We have no physical vertical reference to support a 3 dimensional work space. Boo hiss!

What I want - That Z moves to somewhere at startup. That the bed moves up or down, I don’t care. I can place a limit switch or 2 at the top and/or bottom of bed travel to limit travel to the point prior to destruction. The limit switch would provide a reference point. Now we have 3 dimensions defined for our 3 dimensional work space. But, as it is, the K40 does nothing with the Z axis.

Huge thanks to anyone who can tell me what I’m missing.

Homing Z is possible in smoothieware, it’s just not enabled in the config file. Generally it’s felt to be a dangerous thing to do in most instances. If you home up, and there’s something on the bed, it could crash into the gantry or carriage and destroy your machine (think about what might happen if the power blipped in the middle of a job). If you home down, your z steps need to be perfectly calibrated in order to have an accurate 0 (which could be difficult depending on the bed type you have). So, in theory it’d be nice to have a referenced Z, but in practice we just don’t need it: To that end, Lightburn defaults to relative Z movements and will effectively assume Z0 is wherever the table is at the time the job is sent.You can, of course, have lightburn operate in absolute Z as well, but it ultimately ends up easier using relative movements since most machines don’t have a way to reference Z anyways.

Thank your getting back to me. My grandson was looking over my shoulder and he said your icon means you don’t like me but I told him not to worry, it’s just your cool icon that you present to everyone. He understood that, because whenever possible his online name is Demolisher. He asked me what kind of name is loather and I assured him it’s just a name, like ours, Butler, but one you may have chosen, we don’t know.

Anyway, I understand the logic behind the default configuration and applaud those choices given the potential for disaster. Even so, I’d like to show the kids how that might work and even demonstrate problems that may occur. Unfortunately, I can’t figure out how to do that.

So, even though we don’t need it, can you help me demonstrate absolute Z with my min and/or max limit switches installed?

Hi Jerry,

We have some documentation in progress to start with:

Setting Up a Z-Table
Installing Z-Table Limit Switches

For LightBurn settings and features:
Z Axis Controls
Z-Offset for Lines
Z-Offset for Fill

Let us know if you have any further questions.

Hi, Starla,

Thanks so much. I look forward to reading these. You’re a great bunch to work with.

I didn’t expect to get more information the easy way, so I did some trials and errors over the weekend and I’m going to be happy with my new setup.


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